<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Flex布局侧轴对齐方式</title>
    <style>
        .box{
            display: flex;
            /* 如果弹性盒子在侧轴方向没有尺寸，才能拉伸 */
            /* align-items: stretch; */

            /* align-items: center; */
            /* align-items: start; */
            /* align-items: end; */
            height: 300px;
            border: 1px solid #000;
        }
        
        /* 控制第二个div，侧轴对齐 */
        .box div:nth-child(2){
            align-self: center;
        }

        .box div{
            width: 200px;
            height: 100px;
            background-color: pink;
        }
    </style>
</head>
<body>
    <div class="box">
        <div>1</div>
        <div>2</div>
        <div>3</div>
    </div>
</body>
</html>